In situ oxide removal, dispersal and drying for silicon SiO2

ABSTRACT

A method of removing silicon-dioxide from silicon powder. The method comprises: providing a silicon powder defined by each particle having a silicon core and a silicon dioxide layer surrounding the silicon core; dispersing the particles in a dispersing solution; adding an etching solution, wherein the etching solution removes the silicon dioxide layer; adding an organic solvent, thereby producing an organic phase and an aqueous phase, the organic phase comprising the silicon cores and the organic solvent, and the aqueous phase comprising the dispersing solution, the etching solution, and the etching by-products; coating each silicon core with an organic material; draining out the aqueous phase; washing the organic phase, wherein the remaining material from the aqueous phase is removed; and providing the silicon powder as a plurality of silicon cores each absent a silicon dioxide layer and having an organic coating.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 61/284,329, filed Dec. 15, 2009 and entitled “MATERIALSPROCESSING,” which is hereby incorporated herein by reference in itsentirety as if set forth herein.

FIELD OF THE INVENTION

The present invention relates generally to the field of powder materialproduction. More specifically, the present invention relates to aprocess for removing oxide from produced metallic powders.

BACKGROUND OF THE INVENTION

This disclosure refers to both particles and powders. These two termsare equivalent, except for the caveat that a singular “powder” refers toa collection of particles. The present invention may apply to a widevariety of powders and particles. Powders that fall within the scope ofthe present invention may include, but are not limited to, any of thefollowing: (a) nano-structured powders(nano-powders), having an averagegrain size less than 250 nanometers and an aspect ratio between one andone million; (b) submicron powders, having an average grain size lessthan 1 micron and an aspect ratio between one and one million; (c)ultra-fine powders, having an average grain size less than 100 micronsand an aspect ratio between one and one million; and (d) fine powders,having an average grain size less than 500 microns and an aspect ratiobetween one and one million.

Powders are used in a wide variety of applications. Currently, metallicpowders (particles having a core that is either a pure metal or a metalalloy) are offered having an oxide shell. FIG. 1 is a cross-sectionalside view of a metallic particle 100 having a metal, or metal alloy,core 102 covered by an oxide layer 104. As seen in FIG. 1, the oxidelayer 104 can be quite thick, accounting for approximately 60%(sometimes more) of the entire size of the particle 100. Thissubstantial oxide shell may be useful in certain applications. However,in other situations, it may be undesirable to have such a significantoxide presence.

SDC Materials, LLC has developed an in situ process that employs the useof flowing plasma and a vacuum system in order to produce particleshaving a reduced oxide layer. FIG. 2 is a cross-sectional side view of ametallic particle 200 resulting from this process. The particle 200 hasa metal, or metal alloy, core 202 covered by an oxide shell 204. As canbe seen by comparing FIG. 2 to FIG. 1, the thickness of oxide layer 204for particle 200 is significantly reduced from the thickness of oxidelayer 104 for particle 100. Using this process, the thickness of theoxide layer can be reduced to less than 10% of the entire particlethickness. While providing a considerable improvement over the particleof FIG. 1, this process still does not achieve complete oxide removalfrom the particle. As a result, this nano-particle 200 may still proveto be undesirable for certain applications.

Currently, there is no way to create metallic particles having nooxygen. Even the best vacuum system has oxygen in it. As a result, theend product might not be sufficient for those who want oxide-freemetallic powder.

What is needed in the art is a method for producing metallic powdersthat do not contain any oxygen.

SUMMARY OF THE INVENTION

The present invention provides a process for producing metallic powdersthat do not contain any oxygen. FIG. 3 is a cross-sectional side view ofa powder particle 300 that is produced using the process of the presentinvention. Particle 300 comprises a metal, or metal alloy, core 302, andis characterized by the absence of an oxide shell, in contrast to theparticles of FIGS. 1 and 2.

In one embodiment, the process of the present invention comprisesproviding a powder defined by a plurality of particles. Each particle inthe plurality of particles has a metallic core and an oxide layersurrounding the metallic core. The plurality of particles are thenetched. This etching serves to remove the oxide layer from each particlein the plurality of particles, leaving only the metallic core. In thisfashion, bare metallic powder has been provided free of any oxide.

Additional steps may then be taken to prepare the powder for itseventual application. Each particle in the etched plurality of particlescan be coated with an organic layer. The etched powder may also bedispersed using a dispersing solution.

The steps of etching, coating and dispersing are performed in situ withthe plurality of particles disposed in liquid, absent any exposure ofthe metallic cores to air both during and in between these steps.

The final product may be provided as a dispersion of particles stored ina liquid. Alternatively, the final product may be provided as a driedand settled powder absent any liquid.

In another embodiment, a method for removing silicon-dioxide fromsilicon powder is provided. The method comprises providing a siliconpowder defined by a plurality of particles. Each particle in theplurality of particles has a silicon core and a silicon dioxide layersurrounding the silicon core. The plurality of particles is dispersed ina dispersing solution, preferably methanol. An etching solution,preferably hydrofluoric acid, is added to the dispersing solution. Theetching solution removes the silicon dioxide layer from each particle.

An organic solvent, such as cyclohexane or toluene, is then added to themixture of the dispersing solution and the etching solution. Theaddition of the organic solvent produces an organic phase and an aqueousphase. The organic phase comprises substantially all of the siliconcores and substantially all of the organic solvent, and the aqueousphase comprises substantially all of the dispersing solution,substantially all of the etching solution, and substantially all of theby-products resulting from the silicon dioxide removal. Each siliconcore in the plurality of particles is then coated with an organicmaterial from the organic solvent. The aqueous phase is drained out andthe organic phase is washed, removing substantially all of the remainingaqueous phase material from the organic phase. The silicon powder canthen be provided as a plurality of silicon cores that are absent asilicon dioxide layer surrounding each silicon core, with each siliconcore having an organic coating. The steps of dispersing, adding anetching solution, adding an organic solvent, coating, draining, andwashing are performed in situ with the plurality of particles disposedin liquid, absent any exposure of the silicon cores to air.

In yet another embodiment, a method for removing copper-oxide fromcopper powder is provided. The method comprises providing a copperpowder defined by a plurality of particles, with each particle in theplurality of particles having a copper core and a copper-oxide layersurrounding the copper core. The plurality of particles are disposed inan etching solution in a container. The etching solution, preferablycomprising acetic acid and water, removes the copper-oxide layer fromeach particle. The etching solution and the by-products resulting fromthe copper-oxide removal are then decanted, and the plurality ofparticles are washed, removing substantially all of the remainingetching solution and substantially all of the by-products from thecontainer holding the plurality of particles.

The washed plurality of particles is disposed in an organic solvent,preferably comprising tetraethylene glycol and water. Each copper corein the plurality of particles is then coated with an organic materialfrom the organic solvent, and the plurality of particles is dispersed inthe organic solvent. The copper powder may then be provided as aplurality of dispersed copper cores that are absent a copper-oxide layersurrounding each copper core, with each copper core having an organiccoating. The steps of dispersing in the etching solution, decanting,washing, disposing in the organic solvent, coating, and dispersing areperformed in situ with the plurality of particles disposed in liquid,absent any exposure of the copper cores to air.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional side view of a powder particle having anoxide shell.

FIG. 2 is a cross-sectional side view of a powder particle having areduced oxide shell.

FIG. 3 is a cross-sectional side view of a powder particle having nooxide shell in accordance with the principles of the present invention.

FIG. 4 is a flowchart illustrating one embodiment of a general work flowin accordance with the present invention.

FIGS. 5A-F illustrate exemplary embodiments of the different powderstates during the general work flow in accordance with the presentinvention.

FIG. 6 is a flowchart illustrating one embodiment of a work flow forsilicon powder in accordance with the present invention.

FIGS. 7A-F illustrate exemplary embodiments of the different powderstates during the silicon powder work flow in accordance with thepresent invention.

FIG. 8 is a flowchart illustrating one embodiment of a work flow forcopper powder in accordance with the present invention.

FIGS. 9A-H illustrate exemplary embodiments of the different powderstates during the copper powder work flow in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The following description is presented to enable one of ordinary skillin the art to make and use the invention and is provided in the contextof a patent application and its requirements. Various modifications tothe described embodiments will be readily apparent to those skilled inthe art and the generic principles herein may be applied to otherembodiments. Thus, the present invention is not intended to be limitedto the embodiment shown but is to be accorded the widest scopeconsistent with the principles and features described herein.

FIG. 4 is a flowchart illustrating one embodiment of a general work flow400 in accordance with the principles of the present invention. At step402, a powder is provided in the form of a plurality of particles havinga metallic core and an oxide layer surrounding the metallic core. Aspreviously mentioned, this metallic core may be a pure metal or a metalalloy. The powder is preferably provided in a dry state. FIG. 5Aillustrates one embodiment of the powder 500 being provided in acontainer as a plurality of particles having a metallic core 502 and anoxide layer 504. Typically, the dry powder 500 is settled at the bottomof the container as shown. It is to be understood that FIGS. 5A-F areonly provided to illustrate the general principles of the presentinvention and should not be used to limit the scope of the claims withrespect to details such as size, shape and quantity.

At step 404, the particles are then etched in situ. This etching servesto remove the oxide layer from each particle in the plurality ofparticles, leaving only the metallic core. Preferably, each one of theplurality of particles retains substantially all of its metallic core.In this fashion, a metallic powder has been produced free of any oxide.In a preferred embodiment, the etching is achieved by disposing thepowder in an etching solution. FIG. 5B illustrates one embodiment of anetching solution 506 being introduced into the container and interactingwith the oxide layer 504 of each particle. The powder 500 can be stirredin the etching solution 506 in order to assist with this interaction.The application of the etching solution 506 may cause the particles tobecome slightly suspended for a period of time before settling. FIG. 5Cillustrates one embodiment of the resulting removal of the oxide layer504 from the metallic core 502 of each particle.

The powder may then go through an in situ coating/dispersion process atstep 406 in order to prepare it for its eventual application. Thecoating process involves coating each particle that has been etched withan organic layer. This coating may be achieved by disposing the etchedpowder in an organic solvent. The dispersion process involves dispersingthe plurality of etched particles. This dispersion may be achieved bydisposing the etched powder in a dispersing solution. While the coatingand dispersing processes are grouped together at step 406, they do notnecessarily need to occur at the same time. The coating may be performedprior to the dispersing, and likewise, the dispersing may be performedprior to the coating. Furthermore, the existence of one does notnecessarily depend on the existence of the other. In fact, theachievement of an oxide-free metallic powder may be achieved in theabsence of either or both of these operations. However, in a preferredembodiment, the powder is both coated and dispersed in order to attainoptimum stability and preparation. FIG. 5D illustrates one embodiment ofa coating and dispersing solution 508 being introduced into thecontainer and interacting with each particle. As a result, the powder isdispersed, and each metallic core 502 becomes coated with an organicmaterial 510, as seen in FIG. 5E.

At step 408, the powder may be provided as a dispersion of particles,with each particle having a metallic core and no oxide shell.Preferably, the powder is maintained as a dispersion in a storageliquid, with each particle having an organic coating surrounding itsmetallic core. This storage liquid may simply be the coating/dispersingsolution or may be some other type of liquid appropriate for storing thepowder.

For certain applications, such as sintering, it may not be desirable toprovide the powder in a liquid. Instead, circumstances may dictate thatthe powder be provided in a dry state. In these situations, theoxide-free particles can be dried in situ at step 410. The powder maythen be provided at step 412 as dried particles, each having a metalliccore, preferably surrounded by an organic coating, and no oxide shell,as seen in FIG. 5F. In the example of sintering, the dried powder maythen be placed in a Spark-Plasma Sintering (SPS) machine having areducing atmosphere. The reducing atmosphere matches the organic layerand serves to reduce the organic layer by burning it off, leaving a puremetallic core and a gas by-product. The metallic cores are then fusedtogether, resulting in an ultra-pure block of metal havingnano-properties.

The present invention may be used for a wide variety of metallicpowders. Such powders may include, but are not limited to, silicon andcopper.

FIG. 6 is a flowchart illustrating one embodiment of a work flow 600 forremoving the oxide layer from silicon powder in accordance with thepresent invention. At step 602, the powder is provided as-produced, witheach particle having a silicon core and a silicon-dioxide shell layer.This silicon core may be pure silicon or a silicon alloy. The powder ispreferably provided in a dry state. FIG. 7A illustrates one embodimentof the powder 700 being provided in a container as a plurality ofparticles having a silicon core 702 and a silicon-dioxide shell 704.Typically, the dry powder 700 is settled at the bottom of the containeras shown. It is to be understood that FIGS. 7A-F are only provided toillustrate the general principles of the present invention and shouldnot be used to limit the scope of the claims with respect to detailssuch as size, shape and quantity.

At step 604, methanol 706 a is added to the container and then stirredin order get a dispersion of particles, as seen in FIG. 7B.

At step 606, a hydrogen fluoride (HF) solution (i.e., hydrofluoric acid)is added to the container in order to remove the oxide. As seen in FIG.7C, the result is a plurality of silicon cores 702 dispersed in amixture 706 b of water, HF and methanol. In a preferred embodiment, thesolution contains approximately 10% HF and is applied to the particlesfor between approximately 1 to 5 minutes at about room temperature.However, it is contemplated that the HF concentration, time applied andenvironment temperature may vary according to the particularcircumstances in which the present invention is being employed.

At step 608, an organic solvent is added to the container. Such organicsolvents may include, but are not limited to, cyclohexane and toluene.As seen in FIG. 7D, the addition of the organic solvent produces anorganic phase 708, having the organic solvent, on top of an aqueousphase 709, having the silicon cores 702 dispersed in theHF/water/methanol mixture, with a sharp interface in between the twophases. Due to their hydrophobic properties, the silicon cores 702 thendiffuse up into the organic phase 708, as seen in FIG. 7E, leaving theHF/water/methanol mixture and any etching products in the aqueous phase709.

At step 610, the aqueous phase 709 is drained out of the container,taking most, if not all, of the HF/water/methanol mixture and etchingproducts with it, and leaving behind the organic phase 708 with thesilicon cores 702 each coated with an organic layer 710, as seen in FIG.7F.

At step 612, the organic phase 708 may be washed with water in order toremove residual HF and any other undesirable polar material. Thiswashing step may be repeated as many times as necessary in order toachieve optimum residue removal. However, in a preferred embodiment, theorganic phase is washed twice with water.

At this point, the process may take two separate paths, either dryingthe particles at step 614 a or dispersing the particles at step 614 b.

At step 614 a, the organic phase is dried down to only the powder in thecontainer. The particles are then immediately stored in a storage liquidat step 616 a, where they may be re-dispersed. The storage liquid iseither in the polar-organic range, such as tetraethylene glycol or otherglycol solvents, or the hydrophobic range. This path allows the powderto be used in water-based applications at step 618 and/or organiccoating applications at step 620.

At step 614 b, a dispersant is added to the washed organic phase,thereby dispersing the particles. The dispersant may then be used as astorage liquid at step 616 b. This path allows the powder to be used inorganic coating applications at step 620.

FIG. 8 is a flowchart illustrating one embodiment of a work flow 800 forremoving the oxide layer from copper powder in accordance with thepresent invention. At step 802, the powder is provided as produced, witheach particle having a copper core and a copper-oxide shell layer. Thiscopper core may be pure copper or a copper alloy. The powder is blackand is preferably provided in a dry state. FIG. 9A illustrates oneembodiment of the powder 900 being provided in a container as aplurality of particles having a copper core 902 and a copper-oxide shell904. Typically, the dry powder 900 is settled at the bottom of thecontainer as shown. It is to be understood that FIGS. 9A-H are onlyprovided to illustrate the general principles of the present inventionand should not be used to limit the scope of the claims with respect todetails such as size, shape and quantity.

At step 804, the powder is treated with acetic acid in water. Themixture of acetic acid and water forms an etching solution that is usedto remove the oxide layer 904 from the copper core 902. In a preferredembodiment, the solution contains approximately 0.1% to 1% acetic acid.However, it is contemplated that a variety of different concentrationsmay be employed. FIG. 9B illustrates one embodiment of the acetic acidsolution 906 being introduced into the container and interacting withthe oxide layer 904 of each particle. The application of the solution906 may cause the particles to become slightly suspended for a period oftime before settling at the bottom of the container. FIG. 9C illustratesone embodiment of the resulting removal of the oxide layer 904 from thecopper core 902 of each particle. The etching products (removedcopper-oxide, etc.) rise to the upper portion of the mixture, while theresulting copper-colored powder resides on the bottom, typically in anon-dispersed arrangement.

At step 806, one or more decantations is performed in order to remove amajority, if not all, of the etching solution and products. As seen inFIG. 9D, any remaining etching solution 906 and/or etching products isminimal.

At step 808, the powder may then be washed with water 907, as seen inFIG. 9E, in order to remove any remaining etching solution or etchingproducts. This washing step may be repeated as many times as necessaryin order to achieve optimum residue removal. However, in a preferredembodiment, the powder is washed twice. Preferably, a minimal amount ofthe washing water 907 is left in the container, as seen in FIG. 9F.

At step 810, the powder is treated with a tetraethylene glycol (or someother glycol solvent) and water solution 908, as seen in FIG. 9G. Theinteraction of this solution 908 with the copper cores 902 forms adispersion of copper cores 902 each having an organic coating 910, asseen in FIG. 9H.

At step 812, the resulting copper particles may be stored in the glycolsolvent and water solution. This powder can maintain the same coppercoloring for weeks without any discoloration.

The present invention has been described in terms of specificembodiments incorporating details to facilitate the understanding ofprinciples of construction and operation of the invention. Suchreference herein to specific embodiments and details thereof is notintended to limit the scope of the claims appended hereto. It will bereadily apparent to one skilled in the art that other variousmodifications may be made in the embodiment chosen for illustrationwithout departing from the spirit and scope of the invention as definedby the claims.

What is claimed is:
 1. A method of removing silicon-dioxide from siliconpowder, the method comprising: providing a silicon powder defined by aplurality of particles, each particle in the plurality of particleshaving a silicon core and a silicon dioxide layer surrounding thesilicon core, the silicon core selected from the group consisting of apure silicon and a silicon alloy; dispersing the plurality of particlesin a dispersing solution; adding an etching solution to the dispersingsolution, wherein the etching solution removes the silicon dioxide layerfrom each particle; after the removal of the silicon dioxide by theetching solution, adding an organic solvent to the mixture of thedispersing solution and the etching solution, wherein the addition ofthe organic solvent produces an organic phase and an aqueous phase, theorganic phase comprising substantially all of the silicon cores andsubstantially all of the organic solvent, and the aqueous phasecomprising substantially all of the dispersing solution, substantiallyall of the etching solution, and substantially all of the by-productsresulting from the silicon dioxide removal; coating each silicon core inthe plurality of particles with an organic material from the organicsolvent; draining out the aqueous phase; washing the organic phase,wherein substantially all of the remaining material from the aqueousphase is removed from the organic phase; drying the coated siliconcores; and re-dispersing the dried and coated silicon cores in a storageliquid; wherein the steps of dispersing, adding an etching solution,adding an organic solvent, coating, draining, and washing are performedin situ with the plurality of particles disposed in liquid, absent anyexposure of the silicon cores to air.
 2. The method of claim 1, whereinthe dispersing solution is methanol.
 3. The method of claim 1, whereinthe etching solution is hydrofluoric acid.
 4. The method of claim 3,wherein the etching solution comprises approximately 10% hydrogenfluoride.
 5. The method of claim 4, wherein the step of adding theetching solution comprises disposing the plurality of particles in theetching solution for between approximately one to five minutes atapproximately room temperature.
 6. The method of claim 1, wherein theremoval of the silicon dioxide layer from each particle comprises eachparticle retaining substantially all of the silicon core.
 7. The methodof claim 1, wherein the organic solvent is cyclohexane.
 8. The method ofclaim 1, wherein the organic solvent is toluene.
 9. The method of claim1, wherein the step of adding an organic solvent further comprises: theorganic phase forming on top of the aqueous phase; and the silicon coresdiffusing up from the aqueous phase into the organic phase.
 10. Themethod of claim 1, wherein the storage liquid is a glycol solvent. 11.The method of claim 10, wherein the storage liquid is tetraethyleneglycol.
 12. The method of claim 1, wherein the silicon powder is anano-powder having an average grain size less than 250 nanometers. 13.The method of claim 1, wherein the silicon powder is a submicron powderhaving an average grain size less than 1 micron.
 14. The method of claim1, wherein the silicon powder is ultra-fine powder having an averagegrain size less than 100 microns.
 15. The method of claim 1, wherein thesilicon powder is fine powder having an average grain size less than 500microns.
 16. A method of removing silicon-dioxide from silicon powder,the method comprising: providing a silicon powder defined by a pluralityof particles, each particle in the plurality of particles having asilicon core and a silicon dioxide layer surrounding the silicon core,the silicon core selected from the group consisting of a pure siliconand a silicon alloy; dispersing the plurality of particles in adispersing solution; adding an etching solution to the dispersingsolution, wherein the etching solution removes the silicon dioxide layerfrom each particle; after the removal of the silicon dioxide by theetching solution, adding an organic solvent to the mixture of thedispersing solution and the etching solution, wherein the addition ofthe organic solvent produces an organic phase and an aqueous phase, theorganic phase comprising substantially all of the silicon cores andsubstantially all of the organic solvent, and the aqueous phasecomprising substantially all of the dispersing solution, substantiallyall of the etching solution, and substantially all of the by-productsresulting from the silicon dioxide removal; coating each silicon core inthe plurality of particles with an organic material from the organicsolvent; draining out the aqueous phase; washing the organic phase,wherein substantially all of the remaining material from the aqueousphase is removed from the organic phase; drying the silicon cores;re-dispersing the coated silicon cores in a dispersant; and storing there-dispersed and coated silicon cores in the dispersant; wherein thesteps of dispersing, adding an etching solution, adding an organicsolvent, coating, draining, and washing are performed in situ with theplurality of particles disposed in liquid, absent any exposure of thesilicon cores to air.
 17. A method of removing silicon-dioxide fromsilicon powder, the method comprising: providing a silicon powderdefined by a plurality of particles, each particle in the plurality ofparticles having a silicon core and a silicon dioxide layer surroundingthe silicon core, the silicon core selected from the group consisting ofa pure silicon and a silicon alloy; dispersing the plurality ofparticles in a methanol solution; adding hydrofluoric acid to themethanol solution, wherein the hydrofluoric acid removes the silicondioxide layer from each particle, with each particle retainingsubstantially all of the silicon core; after the removal of the silicondioxide by the methanol solution including hydrofluoric acid, adding anorganic solvent to the mixture of methanol solution includinghydrofluoric acid, wherein the addition of the organic solvent producesan organic phase on top of an aqueous phase, the organic phasecomprising substantially all of the silicon cores and substantially allof the organic solvent, and the aqueous phase comprising substantiallyall of the methanol solution, substantially all of the hydrofluoricacid, and substantially all of the by-products resulting from thesilicon dioxide removal; coating each silicon core in the plurality ofparticles with an organic material from the organic solvent; drainingout the aqueous phase; washing the organic phase, wherein substantiallyall of the remaining material from the aqueous phase is removed from theorganic phase; drying the coated silicon cores; and re-dispersing thedried and coated silicon cores in a storage liquid; wherein the steps ofdispersing, adding hydrofluoric acid, adding an organic solvent,coating, draining, and washing are performed in situ with the pluralityof particles disposed in liquid, absent any exposure of the siliconcores to air.
 18. The method of claim 17, wherein the hydrofluoric acidcomprises approximately 10% hydrogen fluoride.
 19. The method of claim18, wherein the step of adding the hydrofluoric acid comprises disposingthe plurality of particles in the hydrofluoric acid for betweenapproximately one to five minutes at about room temperature.
 20. Themethod of claim 17, wherein the organic solvent is cyclohexane.
 21. Themethod of claim 17, wherein the organic solvent is toluene.
 22. Themethod of claim 17, wherein the storage liquid is a glycol solvent. 23.The method of claim 22, wherein the storage liquid is tetraethyleneglycol.
 24. The method of claim 17, wherein the silicon powder is anano-powder having an average grain size less than 250 nanometers. 25.The method of claim 17, wherein the silicon powder is a submicron powderhaving an average grain size less than 1 micron.
 26. The method of claim17, wherein the silicon powder is ultra-fine powder having an averagegrain size less than 100 microns.
 27. The method of claim 17, whereinthe silicon powder is fine powder having an average grain size less than500 microns.
 28. A method of removing silicon-dioxide from siliconpowder, the method comprising: providing a silicon powder defined by aplurality of particles, each particle in the plurality of particleshaving a silicon core and a silicon dioxide layer surrounding thesilicon core, the silicon core selected from the group consisting of apure silicon and a silicon alloy; dispersing the plurality of particlesin a methanol solution; adding hydrofluoric acid to the methanolsolution, wherein the hydrofluoric acid removes the silicon dioxidelayer from each particle, with each particle retaining substantially allof the silicon core; after the removal of the silicon dioxide by themethanol solution including hydrofluoric acid, adding an organic solventto the mixture of dispersing solution and the etching solution, whereinthe addition of the organic solvent produces an organic phase on top ofan aqueous phase, the organic phase comprising substantially all of thesilicon cores and substantially all of the organic solvent, and theaqueous phase comprising substantially all of the methanol solution,substantially all of the hydrofluoric acid, and substantially all of theby-products resulting from the silicon dioxide removal; coating eachsilicon core in the plurality of particles with an organic material fromthe organic solvent; draining out the aqueous phase; washing the organicphase, wherein substantially all of the remaining material from theaqueous phase is removed from the organic phase; drying the coatedsilicon cores; re-dispersing the coated silicon cores in a dispersant;and storing the re-dispersed and coated silicon cores in the dispersant;wherein the steps of dispersing, adding hydrofluoric acid, adding anorganic solvent, coating, draining, and washing are performed in situwith the plurality of particles disposed in liquid, absent any exposureof the silicon cores to air.